Frame Dimensions, Number of Lines, and Resolution

A video frame is composed of lines. In digital video, each line is sampled to create a number of pixels (samples) per line. The more lines per frame, the higher the image resolution. The more pixels per line, the higher the resolution of each line.

Number of Lines

NTSC uses 525 lines, whereas PAL uses 625. In analog video, many lines are not actually used for picture information, so the total numbers relevant for the picture are somewhat smaller: 486 lines for NTSC and 576 lines for PAL. HD formats defined by the ATSC have either 1080 or 720 active picture lines per frame.

Pixels per Line

In digital video formats, each line is sampled a number of times. In an attempt to create a single digital VTR that could digitize and record both NTSC and PAL signals, the ITU-R BT.601 specification uses 720 samples per line for both NTSC and PAL video. Therefore, a digital NTSC video frame is 720 pixels x 486 lines, and a PAL video frame is 720 pixels x 576 lines.

HD video with 1080 lines uses 1920 pixels per line (1920 x 1080). HD video with 720 lines uses 1280 pixels per line (1280 x 720). Both of these formats have an aspect ratio of 16:9.

Common video frame sizes are shown in the table below.

Width
Height
Pixel aspect ratio
Screen aspect ratio
Description
320
240
1:1
4:3
Used for web distribution or offline video editing.
640
480
1:1
4:3
An early standard for analog-to-digital video editing, and an ATSC video specification.
7201
480
Height greater than width
4:3
NTSC DV and DVD image dimensions. Also part of the ATSC video specification.
7201
486
Height greater than width
4:3
NTSC SD video dimensions used for professional digital formats such as Digital Betacam, D-1, and D-5.
7201
576
Width greater than height
4:3
PAL SD video dimensions used for digital formats such as Digital Betacam, D-1, and D5, as well as DVD and DV.
1280
720
1:1
16:9
An HD video format, capable of higher frame rates in exchange for smaller image dimensions.
1920
1080
1:1
16:9
An HD video format with very high resolution.
960
720
4:3
16:9
Some 720p formats (such as DVCPRO HD and HDV) subsample 1280 pixels to 960 to minimize the data rate.
1440
1280
1080
4:3
3:2
16:9
Some 1080-line formats (such as HDV and DVCPRO HD) subsample 1920 pixels to 1440 or even 1280 to minimize the data rate.

In most video devices, only 704 or 708 pixels are actually used for picture information.

Note: For information on pixels per line and aspect ratios in digital cinema formats such as REDCODE, see Professional Formats and Workflows, available in Final Cut Pro Help.

720 x 486 Versus 720 x 480

One issue that comes up during post-production is the subtle difference between NTSC SD formats that use 486 lines per frame (such as Digital Betacam, D-1, and D-5) and formats that use 480 lines per frame (such as DV, DVCPRO, and DVD). Why is there this subtle difference? The reason is simple: 480 is divisible by 16, and 486 isn’t. Divisibility by 16 is convenient for certain block-based codecs because each frame is broken into 16 x 16 pixel blocks (known as macroblocks) during compression.

The only time this should be a concern is when you are converting between a 486-line format like Digital Betacam and a 480-line format like DVD. However, the extra six lines are typically not visible on an analog television.